1. Field of the Invention
The present invention relates to a PFC (power factor correction) LED (light emitting diode) driver, especially to a PFC LED driver capable of reducing flicker.
2. Description of the Related Art
In present LED lighting applications, LED drivers are generally required to provide a PFC (power factor correction) function, that is, to make an input current in phase with a full-wave-rectified line input voltage. However, an output current flowing through an LED module will thereby tend to have a large current ripple, which causes an annoying flicker phenomenon and degrades luminous efficiency.
To reduce the current ripple of an LED current, one solution is to utilize a two-stage PFC architecture. Please refer to FIG. 1, which illustrates a block diagram of a prior art LED driver having a two-stage PFC architecture. As illustrated in FIG. 1, the prior art LED driver includes a bridge rectifier 110, a PFC converter 120, a bulk capacitor 130, and a PWM converter 140, and an LED module 150 is driven by the prior art LED driver.
The bridge rectifier 110 is used to generate a full-wave-rectified line input voltage VIN according to an AC power VAC.
The PFC converter 120 is used to force an input current IIN to track the full-wave-rectified line input voltage VIN to achieve power factor correction, and at the same time provide a loosely regulated DC voltage VB on the bulk capacitor 130.
The PWM converter 140, of which the operation is independent of that of the PFC converter 120, is used to convert the loosely regulated DC voltage VB to a DC current IOUT to drive the LED module 150.
Although the two-stage PFC architecture is capable of providing a required power factor and reducing the current ripple of an output current, and thereby the flicker, for an LED module, it has the disadvantages of being expensive and bulky.
Another solution is to utilize a single stage PFC constant average current converter to drive an LED module with a very large capacitor in parallel with the LED module. The single stage PFC constant average current converter is responsible for forcing an input current to track a full-wave-rectified line input voltage and regulating the average value of an output current at a preset value for the LED module, and the very large capacitor is responsible for reducing the current ripple of the output current. However, the very large capacitor is bulky and its performance on ripple reduction is still not good enough.
To solve the foregoing problems, a novel PFC LED driver is needed.